Process for increasing the cetane index of distillate obtained from the hydroprocessing of residua

Abstract

A metal- and/or sulfur contaminated charge stock containing residua is hydrotreated in a first reaction zone in the presence of a hydrotreating catalyst comprising a hydrogenating component selected from the Group VIB and Group VIII metals, preferably a combination of nickel and molybdenum, on a refractory support, preferably alumina or silica-alumina, to reduce the metal and/or sulfur content thereof, the demetalated and/or desulfurized residua is hydrocracked in a second reaction zone in the presence of a hydrocracking catalyst comprising a nickel and tungsten impregnated rare earth exchanged zeolite X in combination with a nickel and tungsten impregnated silica-alumina matrix to provide distillate of higher cetane index than that achieved with hydrotreatment alone, and the liquid effluent from said second reaction zone is thereafter passed to a third reaction zone containing a hydrotreating catalyst which is the same as, or is different from, the hydrotreating catalyst in the first reaction zone to effect further hydrotreatment.

What is claimed is: 
     
       1. A process for increasing the cetane index of distillate obtained from the hydroprocessing of petroleum residua which comprises passing a mixture of hydrogen and a metal- and/or sulfur-contaminated charge stock containing residua at a hydrogen partial pressure of from about 1,000 to about 3,000 psia a temperature of from about 650° F. to about 875° F. and a space velocity of from about 0.1 to about 2.0 LHSV through trickle beds of catalyst disposed in three sequential reaction zones, said first reaction zone containing a bed of at least one hydrotreating catalyst comprising a hydrogenating component selected from the group consisting of Group VIB and Group VIII metals and combinations thereof on a refractory support, said second reaction zone containing a bed of hydrocracking catalyst comprising a nickel-tungsten impregnated rare earth exchanged zeolite X component in combination with a nickel-tungsten impregnated silica-alumina matrix, and said third reaction zone containing a bed of at least one hydrotreating catalyst, the same or different from the hydrotreating catalyst in said first zone, comprising a hydrogenating component selected from the group consisting of Group VIB and Group VIII metals and combinations thereof on a refractory support thereby providing a distillate having a cetane index of at least about 50. 
     
     
       2. The process of claim 1 wherein said upgrading is carried out in ebullating catalyst bed reactors, in which at least three reactors are employed such that each catalyst employs a separate reactor and the processing maintains the same catalyst sequence. 
     
     
       3. The process of claim 1 wherein the charge stock is substantially composed of residual hydrocarbons boiling above about 900° F. 
     
     
       4. The process of claim 1 wherein the charge stock is introduced at a hydrogen partial pressure of from about 1,500 to about 2,500 psi, a temperature of from about 700° F. to about 825° F. and a space velocity of from about 0.15 to about 0.75 LHSV. 
     
     
       5. The process of claim 1 wherein said three sequential zones are contained in one reactor. 
     
     
       6. The process of claim 1 wherein the hydrotreating catalyst in the first and third reaction zones comprises nickel and molybdenum on a refractory support. 
     
     
       7. The process of claim 6 wherein said refractory support is alumina, silica, silica alumina, titania, zirconia, chronia, or combinations thereof. 
     
     
       8. The process of claim 6 wherein said refractory support is manganese modules, bog manganese, bog iron, ferrite, pyrite, arsenopyrite, niccolite, diatomaceous earth, quartz, or combinations thereof. 
     
     
       9. The process of claim 1 wherein there are at least two hydrotreating catalysts in said first reaction zone arranged in superimposed levels with the hydrotreating catalyst in the upper level possessing a relatively large sized average pore diameter and the hydrotreating catalyst in the lower level possessing a relatively imtermediate sized average pore diameter, it being further provided that the hydrotreating catalyst in the third reaction zone possesses a relatively small sized average pore diameter. 
     
     
       10. The process of claim 9 wherein the average pore diameter of the hydrocracking catalysts in the upper and lower levels of the first reaction zone are from about 160 to about 200 A and from about 100 to about 140 A, respectively, and the average pore diameter of the hydrocracking catalyst in the third reaction zone is from about 60 to about 95 A. 
     
     
       11. The process of claim 1 wherein the total metal content of the hydrotreating catalyst in the first and third reaction zones is from about 10 to about 30 weight percent of the catalyst. 
     
     
       12. The process of claim 6 wherein the nickel is present at a level of from about 2 to about 5 weight percent, and the molybdenum is present at a level of from about 8 to about 25 weight percent, of the catalyst. 
     
     
       13. The process of claim 1 wherein the total content of nickel and tungsten in the hydrocracking catalyst is from 10 to about 20 weight percent of the catalyst. 
     
     
       14. The process of claim 13 wherein the nickel is present at a level of from about 2 to about 5 weight percent, and the tungsten is present at a level of from about 8 to about 15 weight percent, of the catalyst. 
     
     
       15. The process of claim 1 wherein the cetane index of the product middle distillate is at least about 60. 
     
     
       16. The process of claim 1 wherein the cetane index of the product middle distillate is at least about 70. 
     
     
       17. The process of claim 1 wherein the volumetric ratio of the catalyst in the first, second and third reaction zones is about 6:1:3. 
     
     
       18. The process of claim 9 or 10 wherein the volumetric ratio of the hydrotreating catalyst in the upper level of the first reaction zone to the hydrotreating catalyst in the lower level of the first reaction zone is about 1:1. 
     
     
       19. The process of claim 18 wherein the volumetric ratio of the first, second and third reaction zones is about 6:1:3.